You probably know about this already, but just on the off-chance you hadn't heard about it already:

Humble Bundle currently have a bundle of puzzle e-books available. Humble Bundle work on a "pay what you want, and you can choose to donate it to a charity of your choice" system; as far as I can tell, any charity with a UK charity number is eligible for your donation, though I like the look of the three defaults which are suggested.

Pay/donate US$1 or more and you receive links to download .pdf versions of seven books; most likely to be of interest here is "Logical Leaps and Landings: An Adalogical Ænigmas Collection" by Pavel Curtis, descirbed as follows: "Think you're up for a truly serious test of your logical-reasoning powers? Every month, Augusta Ada King, Countess of Lovelace, often credited at the world's first computer programmer, presents to the solving public (with clerical assistance from Pavel Curtis) a new logical "ænigma". This book collects the first two years of Ada's series, 24 logic puzzles ranging from challenging to exceedingly difficult. Each puzzle is accompanied by author commentary and a full solution, along with explanations of how to read any Easter eggs that Ada might have concealed somewhere on the page. NEW FOR THIS BUNDLE."

Pay/donate US$7 or more and you get eight more books in the same way for a total of fifteen, headlined by Dr. Thomas Snyder's "The Art of Sudoku" and Mike Selinker's "The Maze of Games". Increase your payment/donation to US$15 and up for a total of twenty-one books plus the audiobook version of "The Maze of Games" and one more, containing puzzles pointing to hints to a super-meta for "The Maze of Games", once it is written in a couple of months' time. Increase your payment/donation to US$42 or more and US$25.01 of it will cover the cost of a hardback copy of "The Maze of Games", but you have to pay shipping on top... and shipping a hardback book overseas is seriously expensive, raising the effective price past the GBP 50 mark.

Being cynical to a fault, it looks like several of these books could not actually have previously been bought as dead-tree books (except possibly via print-on-demand services...?) and it's possible that several of the puzzles may well have been published elsewhere previously, but you're still getting an awful lot of high-quality puzzles for a remarkably low cost.... which could be entirely a charity donation if you wanted it to be one. Having had a look, there's enough to be of interest to people who only like logic puzzles, and people who like other sorts of puzzles as well will be in heaven.